Guides
Plain-English, source-cited guides behind our apps.
Cold plunge
Chlorine vs. hydrogen peroxide: the dosing math
Pick a sanitizer, the per-fill dosing numbers, and the one mix you must never make.
How often should you change cold plunge water?
A cadence chart by tub type and sanitizer, plus when to clean the filter.
Hot tub
Hot tub water balance cheat sheet
Ideal levels for chlorine, bromine, pH, alkalinity, and hardness — and the order to adjust them.
How much chlorine (or bromine) to add
The per-gallon dosing math, after-soak top-ups, and weekly shock, with a worked example.
Reef aquarium
Why dose magnesium before calcium and alkalinity
If Ca and Alk won't hold, low Mg is usually why — the chemistry, dosing order, and targets.
Reef tank target parameters by tank type
Ca, Alk, Mg, pH, nitrate, phosphate, and salinity targets for SPS, mixed, and LPS/soft tanks.
Pizza dough
How much yeast for cold-ferment pizza dough?
A baker's-percentage chart for 24/48/72-hour cold ferments, plus yeast conversions.
Pizza dough hydration by style
Hydration, salt, oil, and ball weight for Neapolitan, NY, Detroit, Sicilian, and Roman.
Planted aquarium
EI vs. PPS-Pro vs. PMDD: which dosing method?
The three planted-tank fertilizer methods compared — schedule, water changes, and who each suits.
The PPS-Pro recipe and dosing schedule
The exact two-bottle macro/micro mix and the daily dosing rate.
Pottery glaze
UMF glaze chemistry explained
What the Unity Molecular Formula tells you — oxide groups, unity, and the silica:alumina ratio.
Is your glaze food-safe? Limit formulas and leaching
Limit ranges, why low silica leaches, the crazing link, and the toxic oxides to watch.
Hydroponics
ppm, EC, and the PPM scales explained
EC vs ppm, the 500/700 scales, the 0.7 factor, and why two meters disagree.
Hydroponic nutrient targets by crop and stage
EC and nutrient targets for lettuce, herbs, tomato, cucumber, strawberry — by growth stage.
Home canning
Water bath vs. pressure canning: which one your food needs
The dividing line is acidity (pH 4.6). Per USDA/NCHFP, which foods need which method — and why.
Canning at altitude: how to adjust time and pressure
Why altitude changes home canning, and the USDA adjustments for water-bath time and canner PSI.
Koi pond
Koi pond water parameters: the levels that matter
Targets and danger thresholds for pH, ammonia, nitrite, nitrate, KH, and salt.
Why your koi pond pH crashes — and the KH fix
Why low KH causes overnight pH crashes, and the baking-soda dose that fixes it.
Cold-process soap
Lye calculator basics: how to calculate NaOH
Saponification (SAP) values, why every oil needs a different amount of lye, and how superfat changes the number.
Superfat and water in cold-process soap, explained
What superfat (lye discount) and water amount actually do — the three ways to express water, and how each affects your bar.
Longevity bloodwork
The longevity blood panel: which markers and why
ApoB, Lp(a), hsCRP, HbA1c and the rest — what each one measures, and the published targets named authors cite.
Optimal vs. reference ranges in bloodwork
Why your lab's "normal" reference range describes the population, not your longevity target.
Hard cider
Blending cider apples: sugar, acid, and tannin
The three levers of a cider blend, the Long Ashton apple classes, and target acidity for a balanced hard cider.
YAN and yeast nutrient: preventing H₂S in cider
Why apple juice is low in nitrogen, how deficiency causes rotten-egg H₂S and stuck ferments, and how to dose nutrient.
Jerky safety
Why jerky must reach 160°F (165°F for poultry)
Why drying alone doesn't make jerky safe, the USDA kill-step temperatures, and whether to heat before or after dehydrating.
Curing salt for jerky: how much Prague Powder #1?
What Prague Powder #1 is, the standard nitrite use rate, why precise measurement matters, and how curing fits the heat step.
Mushroom cultivation
Biological efficiency (BE): how to measure mushroom yield
What BE means, the formula, typical figures by species, and why dry substrate weight is the denominator.
Substrate hydration and field capacity
The squeeze test, target moisture by substrate, and why over-wet substrate invites contamination.
Saltwater pool
What salt level does a salt cell need?
Target salt ppm by brand (Hayward, Pentair, Jandy), why too-low and too-high both hurt the cell, and how to adjust.
CSI and salt cell longevity
What the saturation index is, why a balanced index protects your cell and plaster, and the levers that move it.
Chlorine pool
Free chlorine and CYA: the ratio that keeps a pool clear
Why stabilizer changes how much chlorine you need, the FC/CYA target ratio, and why a fixed 1–3 ppm target fails.
How much chlorine or shock to add to a pool
Dosing liquid chlorine or cal-hypo by volume and target FC rise, routine vs. shocking, and clearing algae.
Off-grid solar
How many solar panels do I need?
Size an array from daily watt-hour load, peak sun hours, and system losses — with a worked van/RV example.
What size battery bank for off-grid?
Size a bank from daily load, days of autonomy, and usable depth of discharge — and why LiFePO4 and AGM differ.
Off-grid water
Sizing a well pump: total dynamic head (TDH)
What TDH is, the four components — drawdown, lift, pressure, friction — and how TDH and flow together pick a pump.
UV water disinfection dose (NSF/ANSI 55)
How UV dose works, the Class A 40 mJ/cm² standard, and why flow rate and water clarity decide the real dose.
Knife heat-treat
Quench and temper: hitting a target hardness (HRC)
The austenitize–quench–temper sequence, and how each step sets the final HRC by steel.
Tempering temperature and oxide color chart
What tempering does, the temper-color chart for plain carbon steel, and why a thermostatic oven beats reading colors.
Leatherwork
Stitches per inch (SPI) by leather weight
Matching SPI to leather weight and project, the SPI-to-millimeter conversion, and why proportion matters.
How much thread for a saddle stitch?
A rule of thumb for cutting thread, why thickness and SPI change the multiplier, and how to avoid running short.
Red light therapy
How to calculate red light therapy dose (J/cm²)
Irradiance times time, why distance changes everything, and how to compare panels on real numbers.
Why more red light isn't better: the biphasic dose response
Too little does nothing, an optimal window helps, too much inhibits — and what it means for sessions.
Candle making
How much wax and fragrance for a candle?
Size the wax to the vessel and the fragrance to the wax — and the two limits (wax max and IFRA) that keep a candle safe.
How to choose a candle wick size
Pick a wick series for your wax, size it to the container diameter, adjust for fragrance and dye, then confirm with a test burn.